Method for making composite carbon nanotube structure

ABSTRACT

A method for making a composite carbon nanotube structure includes the following steps. An organic solvent, a polymer, and a carbon nanotube structure are provided. The polymer is dissolved in the organic solvent to obtain a polymer solution. The carbon nanotube structure is soaked with the polymer solution. A contact angle between the organic solvent and a carbon nanotube is less than 90 degrees.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims all benefits accruing under 35 U.S.C. §119 fromChina Patent Application No. 201010212591.0, filed on Jun. 29, 2010, inthe China Intellectual Property Office, the disclosure of which isincorporated herein by reference. This application is related tocommonly-assigned applications entitled, “METHOD FOR MAKING COMPOSITECARBON NANOTUBE STRUCTURE,” filed Dec. 6, 2010 Ser. No. 12/960,644,“COMPOSITE CARBON NANOTUBE STRUCTURE,” filed Dec. 6, 2010 Ser. No.12/960,655, “METHOD FOR MAKING COMPOSITE CARBON NANOTUBE STRUCTURE,”filed Dec. 6, 2010 Ser. No. 12/960,658, and “COMPOSITE CARBON NANOTUBESTRUCTURE,” filed Dec. 6, 2010 Ser. No. 12/960,662.

BACKGROUND

1. Technical Field

The present disclosure relates to a method for making a composite carbonnanotube structure.

2. Description of Related Art

Carbon nanotubes are tubules of carbon generally having a diameter ofabout 0.5 nanometers to about 100 nanometers, and composed of a numberof coaxial cylinders of graphite sheets. Generally, the carbon nanotubesprepared by conventional methods are in particle or powder forms. Theparticle or powder-shaped carbon nanotubes limit the applications inwhich they can be used. Thus, preparation of macro-scale carbon nanotubestructures, such as carbon nanotube wires, has attracted attention.

A carbon nanotube wire having a macro-scale carbon nanotube structure,is directly drawn from a carbon nanotube array on a substrate. Thecarbon nanotube wire includes a plurality of successive carbon nanotubessubstantially oriented along a same direction. The carbon nanotubesjoined end to end by van der Waals attractive force therebetween.

However, the carbon nanotubes are only joined by the van der Waalsattractive force therebetween, thus a mechanical strength of the carbonnanotube wire needs to be improved.

What is needed, therefore, is to provide a method for making a compositecarbon nanotube structure, to overcome the above-described shortcomings.

BRIEF DESCRIPTION OF THE DRAWINGS

Many aspects of the embodiments can be better understood with referenceto the following drawings. The components in the drawings are notnecessarily drawn to scale, the emphasis instead being placed uponclearly illustrating the principles of the embodiments. Moreover, in thedrawings, like reference numerals designate corresponding partsthroughout the several views.

FIG. 1 shows a Scanning Electron Microscope (SEM) image of a flocculatedcarbon nanotube film.

FIG. 2 shows an SEM image of a pressed carbon nanotube film.

FIG. 3 shows an SEM image of a drawn carbon nanotube film.

FIG. 4 shows an SEM image of a carbon nanotube structure consisting of aplurality of stacked drawn carbon nanotube films.

FIG. 5 shows an SEM image of an untwisted carbon nanotube wire.

FIG. 6 shows a low magnification SEM image of a twisted carbon nanotubewire defined as CNT wire.

FIG. 7 shows a high magnification SEM image of the CNT wire in FIG. 6.

FIG. 8 shows a low magnification SEM image of a shrinking CNT wire.

FIG. 9 shows a high magnification SEM image of the shrinking CNT wire inFIG. 8.

FIG. 10 shows a low magnification SEM image of a composite CNT wire.

FIG. 11 shows a high magnification SEM image of the composite CNT wirein FIG. 10.

FIG. 12 shows a comparison of diameters, tensile strengths, and tensileloads of the CNT wire in FIG. 6, the shrinking CNT wire in FIG. 8, andthe composite CNT wire in FIG. 10.

FIG. 13 shows a comparison of tensile strengths of the CNT wire in FIG.6, the shrinking CNT wire in FIG. 8, and the composite CNT wire in FIG.10, if the three wires have a determined strain quotiety.

FIG. 14 shows a comparison of the tensile strengths of the composite CNTwires soaked with different polymer solutions.

FIG. 15 shows a comparison of the tensile loads and the diameters of thecomposite CNT wires soaked with different polymer solutions.

FIG. 16 shows a comparison of the tensile strengths and the diameters ofthe composite CNT wires soaked with different polymer solutions.

FIG. 17 shows a comparison of the tensile strengths of the composite CNTwires having different carbon nanotubes.

DETAILED DESCRIPTION

The disclosure is illustrated by way of example and not by way oflimitation in the figures of the accompanying drawings in which likereferences indicate similar elements. It should be noted that referencesto “an” or “one” embodiment in this disclosure are not necessarily tothe same embodiment, and such references mean at least one.

A method for making a composite carbon nanotube structure of a firstembodiment can include the following steps:

-   -   S10, providing an organic solvent, a polymer, and a carbon        nanotube structure, wherein the carbon nanotube structure is a        free-standing structure and includes a plurality of carbon        nanotubes, a contact angle between the organic solvent and the        carbon nanotubes being less than 90 degrees;    -   S20, dissolving the polymer in the organic solvent to obtain a        polymer solution; and    -   S30, soaking the carbon nanotube structure with the polymer        solution.

In step S10, the carbon nanotube structure can be a planar structure, alinear structure, or other tridimensional structures. The carbonnanotube structure can be capable of forming a free-standing structure.The term “free-standing structure” can be defined as a structure thatdoes not have to be supported by a substrate. For example, afree-standing structure can sustain the weight of itself when thefree-standing structure is hoisted by a portion thereof without anysignificant damage to its structural integrity. The carbon nanotubesdistributed in the carbon nanotube structure defines a plurality of gapstherebetween. An average gap can be in a range from about 0.2 nanometersto about 9 nanometers. The carbon nanotubes can have a significant vander Waals attractive force therebetween. The free-standing structure ofthe carbon nanotube structure is realized by the carbon nanotubes joinedby van der Waals attractive force. So, if the carbon nanotube structureis placed between two separate supporters, a portion of the carbonnanotube structure, not in contact with the two supporters, would besuspended between the two supporters and yet maintain film structuralintegrity.

The carbon nanotube structure can include a carbon nanotube filmstructure. The carbon nanotubes in the carbon nanotube film structurecan be orderly or disorderly arranged. If the carbon nanotube structureincludes a plurality of carbon nanotube film structures stackedtogether, adjacent carbon nanotube film structures can only be adheredby van der Waals attractive force therebetween.

The term ‘disordered carbon nanotube film structure’ includes, but isnot limited to, a structure where the carbon nanotubes are arrangedalong many different directions such that the number of carbon nanotubesarranged along each different direction can be almost the same (e.g.uniformly disordered), and/or entangled with each other. ‘Ordered carbonnanotube film structure’ includes, but is not limited to, a structurewhere the carbon nanotubes are arranged in a consistently systematicmanner, e.g., the carbon nanotubes are arranged approximately along asame direction and or have two or more sections within each of which thecarbon nanotubes are arranged approximately along a same direction(different sections can have different directions). The carbon nanotubesin the carbon nanotube film structure can be single-walled,double-walled, and/or multi-walled carbon nanotubes.

Macroscopically, the carbon nanotube film structure may have asubstantially planar structure. The planar carbon nanotube structure canhave a thickness of about 0.5 nanometers to about 100 microns. Thecarbon nanotube film structure includes a plurality of carbon nanotubesand defines a plurality of micropores having a size of about 1 nanometerto about 500 nanometers. The carbon nanotube film structure includes atleast one carbon nanotube film, the at least one carbon nanotube filmincluding a plurality of carbon nanotubes substantially parallel to asurface of the corresponding carbon nanotube film.

The carbon nanotube film structure can include a flocculated carbonnanotube film as shown in FIG. 1. The flocculated carbon nanotube filmcan include a plurality of long, curved, disordered carbon nanotubesentangled with each other and can form a free-standing structure.Further, the flocculated carbon nanotube film can be isotropic. Thecarbon nanotubes can be substantially uniformly dispersed in the carbonnanotube film. The adjacent carbon nanotubes are acted upon by the vander Waals attractive force therebetween, thereby forming an entangledstructure with micropores defined therein. Alternatively, theflocculated carbon nanotube film is very porous. Sizes of the microporescan be about 1 nanometer to about 500 nanometers. Further, due to thecarbon nanotubes in the carbon nanotube structure being entangled witheach other, the carbon nanotube structure employing the flocculatedcarbon nanotube film has excellent durability and can be fashioned intodesired shapes with a low risk to the integrity of the carbon nanotubestructure. The flocculated carbon nanotube film, in some embodiments,will not require the use of a structural support due to the carbonnanotubes being entangled and adhered together by van der Waalsattractive force therebetween. The flocculated carbon nanotube film candefine a plurality of micropores having a diameter of about 1 nanometerto about 500 nanometers. The micropores defined in the flocculatedcarbon nanotube film can improve a special surface area of theflocculated carbon nanotube film. More polymer solution can beaccommodated in the flocculated carbon nanotube film.

The carbon nanotube film structure can include a pressed carbon nanotubefilm. The carbon nanotubes in the pressed carbon nanotube film can bearranged along a same direction or arranged along different directions.The carbon nanotubes in the pressed carbon nanotube film can rest uponeach other. The adjacent carbon nanotubes are combined and attracted toeach other by van der Waals attractive force, and can form afree-standing structure. An angle between a primary alignment directionof the carbon nanotubes and a surface of the pressed carbon nanotubefilm can be in an range from approximately 0 degrees to approximately 15degrees. The pressed carbon nanotube film can be formed by pressing acarbon nanotube array. The angle is closely related to pressure appliedto the carbon nanotube array. The greater the pressure, the smaller theangle. The carbon nanotubes in the carbon nanotube film is substantiallyparallel to the surface of the carbon nanotube film if the angle isabout 0 degrees. A length and a width of the carbon nanotube film can beset as desired. The pressed carbon nanotube film can include a pluralityof carbon nanotubes substantially aligned along one or more directions.The pressed carbon nanotube film can be obtained by pressing the carbonnanotube array with a pressure head. Alternatively, the shape of thepressure head and the pressing direction can determine the direction ofthe carbon nanotubes arranged therein. Specifically, in one embodiment,a planar pressure head is used to press the carbon nanotube array alongthe direction substantially perpendicular to a substrate. A plurality ofcarbon nanotubes pressed by the planar pressure head may be sloped inmany directions. In another embodiment, as shown in FIG. 2, if aroller-shaped pressure head is used to press the carbon nanotube arrayalong a certain direction, the pressed carbon nanotube film having aplurality of carbon nanotubes substantially aligned along the certaindirection can be obtained. In another embodiment, if the roller-shapedpressure head is used to press the carbon nanotube array along differentdirections, the pressed carbon nanotube film having a plurality ofcarbon nanotubes substantially aligned along different directions can beobtained. The pressed carbon nanotube film can define a plurality ofmicropores having a diameter of about 1 nanometer to about 500nanometers. The micropores defined in the pressed carbon nanotube filmcan improve a special surface area of the pressed carbon nanotube film.More polymer solution can be accommodated in the flocculated carbonnanotube film.

In some embodiments, the carbon nanotube film structure includes atleast one drawn carbon nanotube film as shown in FIG. 3. The drawncarbon nanotube film can have a thickness of about 0.5 nanometers toabout 100 microns. The drawn carbon nanotube film includes a pluralityof carbon nanotubes that can be arranged substantially parallel to asurface of the drawn carbon nanotube film. A plurality of microporeshaving a size of about 1 nanometer to about 500 nanometers can bedefined by the carbon nanotubes. A large number of the carbon nanotubesin the drawn carbon nanotube film can be oriented along a preferredorientation, meaning that a large number of the carbon nanotubes in thedrawn carbon nanotube film are arranged substantially along the samedirection. An end of one carbon nanotube is joined to another end of anadjacent carbon nanotube arranged substantially along the samedirection, by van der Waals attractive force. More specifically, thedrawn carbon nanotube film includes a plurality of successively orientedcarbon nanotube segments joined end-to-end by van der Waals attractiveforce therebetween. Each carbon nanotube segment includes a plurality ofcarbon nanotubes substantially parallel to each other and joined by vander Waals attractive force therebetween. The carbon nanotube segmentscan vary in width, thickness, uniformity, and shape. A small number ofthe carbon nanotubes are randomly arranged in the drawn carbon nanotubefilm and has a small if not negligible effect on the larger number ofthe carbon nanotubes in the drawn carbon nanotube film arrangedsubstantially along the same direction.

Understandably, some variation can occur in the orientation of thecarbon nanotubes in the drawn carbon nanotube film as can be seen inFIG. 3. Microscopically, the carbon nanotubes oriented substantiallyalong the same direction may not be perfectly aligned in a straightline, and some curve portions may exist. Furthermore, it can beunderstood that some carbon nanotubes are located substantially side byside and oriented along the same direction and in contact with eachother.

The carbon nanotube film structure can include a plurality of stackeddrawn carbon nanotube films. Adjacent drawn carbon nanotube films can beadhered by only the van der Waals attractive force therebetween. Anangle can exist between the carbon nanotubes in adjacent drawn carbonnanotube films. The angle between the aligned directions of the adjacentdrawn carbon nanotube films can range from 0 degrees to about 90degrees. In one embodiment, the angle between the aligned directions ofthe adjacent drawn carbon nanotube films is substantially 90 degrees asshown in FIG. 4. Simultaneously, aligned directions of adjacent drawncarbon nanotube films can be substantially perpendicular to each other,thus a plurality of micropores and nodes can be defined by the carbonnanotube film structure. The carbon nanotube film structure including aplurality of uniform micropores and nodes can form a nanoporousstructure. The nanoporous structure can provide a huge surface area toadsorb more polymer solution therein.

The carbon nanotube structure can include a carbon nanotube wire. Thecarbon nanotube wire can include a plurality of carbon nanotubes joinedend to end by van der Waals attractive force therebetween along an axialdirection. The carbon nanotube structure can include a plurality ofcarbon nanotube wires. The carbon nanotube wires can be substantiallyparallel to each other to form a bundle-like structure or twisted witheach other to form a twisted structure. The plurality of carbon nanotubewires can also be woven together to form a woven structure. Thebundle-like structure, the twisted structure, and the woven structureare three kinds of linear shaped carbon nanotube structure.

The carbon nanotube wire can be untwisted or twisted. Treating the drawncarbon nanotube film with a volatile solvent can obtain the untwistedcarbon nanotube wire. In one embodiment, the volatile solvent can beapplied to soak the entire surface of the drawn carbon nanotube film.During the soaking, adjacent substantially parallel carbon nanotubes inthe drawn carbon nanotube film will bundle together due to the surfacetension of the volatile solvent as it volatilizes, and thus the drawncarbon nanotube film will be shrunk into an untwisted carbon nanotubewire. The untwisted carbon nanotube wire includes a plurality of carbonnanotubes substantially oriented along a same direction (i.e., adirection along the length direction of the untwisted carbon nanotubewire) as shown in FIG. 5. The carbon nanotubes are substantiallyparallel to the axis of the untwisted carbon nanotube wire. In oneembodiment, the untwisted carbon nanotube wire includes a plurality ofsuccessive carbon nanotubes joined end to end by van der Waalsattractive force therebetween. The length of the untwisted carbonnanotube wire can be arbitrarily set as desired. A diameter of theuntwisted carbon nanotube wire ranges from about 0.5 nanometers to about100 micrometers.

The twisted carbon nanotube wire can be obtained by twisting a drawncarbon nanotube film using a mechanical force to turn the two ends ofthe drawn carbon nanotube film in opposite directions. The twistedcarbon nanotube wire includes a plurality of carbon nanotubes helicallyoriented around an axial direction of the twisted carbon nanotube wireas shown in FIG. 6. In one embodiment, the twisted carbon nanotube wireincludes a plurality of successive carbon nanotubes joined end to end byvan der Waals attractive force therebetween. The length of the carbonnanotube wire can be set as desired. A diameter of the twisted carbonnanotube wire can be from about 0.5 nanometers to about 100 micrometers.

The organic solvent can be polyacrylonitrile, polyvinyl alcohol (PVA),polypropylene (PP), polystyrene (PS), polyvinylchloride (PVC),polyethylene terephthalate (PET), or combinations thereof. A kind and apolymerization degree of the polymer are not limited provided thepolymer can be dissolved in the organic solvent. The greater the degreeof polymerization, the greater the mechanical strength of the polymerand the less a solubility of the polymer. In one embodiment, the polymeris polyvinyl alcohol, having a polymerization degree from about 1500 toabout 3500.

The organic solvent is configured to dissolve the polymer therein andsoak the carbon nanotube structure. The contact angle between theorganic solvent and the carbon nanotubes can be less than 90 degrees,thus the polymer solution can even soak inner surfaces of the carbonnanotubes. The contact angle is the angle at which a liquid interfacemeets a solid surface. The contact angle is also a quantitative measureof a wetting of the solid by the liquid. Wettability between the organicsolvent and the carbon nanotubes can be determined by the contact anglebetween the organic solvent and the carbon nanotubes. The less thecontact angle, the better the soakage capability of the organic solventand the better the wettability between the organic solvent and thecarbon nanotubes. In one embodiment, the contact angle is less than 70degrees. The organic solvent can have a surface tension greater than 20millimeters per newton, thus, the organic solvent can shrink the carbonnanotube structure soaked therein. The greater the surface tension, thegreater a shrinking strength of the organic solvent and the polymersolution, and the tighter the polymer adhering to the carbon nanotubestructure. In one embodiment, the surface tension of the organic solventis greater than or equal to about 40 millimeters per newton. The organicsolvent can be dimethyl sulphoxide (DMSO), dimethyl formamide (DMF), 2,5-dimethyl furan, or combinations thereof. In one embodiment, thepolymer is PVA and the organic solvent is DMSO. The contact anglebetween the DMSO and the carbon nanotubes is about 70 degrees. Thesurface tension of the DMSO is about 43.54 millimeters per newton.

In step S20, a mass ratio between the polymer and the polymer solutioncan be moderate, thus more polymer in the polymer solution caninfiltrate into intertube spaces inside the carbon nanotube structure.The intertube spaces can include spaces defined among the carbonnanotubes and spaces defined by the inner surfaces of the carbonnanotubes. In one embodiment, the organic solvent is DMSO, the polymeris PVA, and the mass ratio between the PVA and the polymer solution isin a range from about 1 percent to about 9 percent.

In step S30, if the carbon nanotube structure is soaked by the polymersolution, the organic solvent will wet the carbon nanotube structure.The polymer loaded by the organic solvent can infiltrate into theintertube spaces in the carbon nanotube structure and integrate with thecarbon nanotube structure firmly. The carbon nanotubes can be joined bythe polymer and the van der Waals attractive force therebetween at thesame time. A mechanical strength of the carbon nanotube structure can beimproved. A composite carbon nanotube structure can be obtained bycompositing the carbon nanotube structure and the polymer. In thecomposite carbon nanotube structure, the intertube spaces in the carbonnanotube structure can be reduced by filling the polymer. The organicsolvent can play an important role to obtain a composite carbon nanotubestructure having a greater mechanical strength. The less the contactangle between the organic solvent, the more the polymer infiltrates intothe intertube spaces, the firmer the polymer adheres to the carbonnanotubes, and the greater the mechanical strength of the compositecarbon nanotube structure.

A shrinking effect of the organic solvent can also reduce the intertubespaces in the carbon nanotube structure. A volume of the compositecarbon nanotube structure can be less than a volume of the carbonnanotube structure. A density of the composite carbon nanotube structurecan be greater than a density of the carbon nanotube structure. Amechanical strength of the composite carbon nanotube structure can begreater than a mechanical strength of the carbon nanotube structure. Thegreater the surface tension, the greater the density of the compositecarbon nanotube structure, and the greater the mechanical strength ofthe composite carbon nanotube structure.

The method for making the composite carbon nanotube structure canfurther include a step of vaporizing the organic solvent from thecomposite carbon nanotube structure composited by the polymer and thecarbon nanotube structure. The means for vaporizing the organic solventis not limited, provided the organic solvent in the carbon nanotubestructure is vaporized, and the polymer and the carbon nanotubes are notoxidized. When the organic solvent in the carbon nanotube structure isvaporized, a mass ratio between the polymer in the composite carbonnanotube structure and the composite carbon nanotube structure can be inrange from about 2.5 percent to about 21.5 percent.

A method for making a composite carbon nanotube structure of a secondembodiment can include the following steps:

-   -   S210, providing an organic solvent, a pre-polymer, and a carbon        nanotube structure, wherein the carbon nanotube structure is a        free-standing structure and includes a plurality of carbon        nanotubes, a contact angle between the organic solvent and the        carbon nanotubes being less than 90 degrees;    -   S220, dissolving the pre-polymer in the organic solvent to        obtain a polymer solution;    -   S230, soaking the carbon nanotube structure with the pre-polymer        solution; and    -   S240, polymerizing the pre-polymer infiltrated into the carbon        nanotube structure to obtain a polymer.

The steps, features, and functions of the method of the secondembodiment are similar to the method of the first embodiment. Thedifference is that the polymer infiltrated into the intertube spaces ofthe carbon nanotube structure is polymerized by the pre-polymerinfiltrated into the intertube spaces.

A molecular weight of the pre-polymer can be less than a molecularweight of the polymer. A solubility of the pre-polymer in the organicsolvent can be greater than a solubility of the polymer in the organicsolvent. If the pre-polymer and the polymer are dissolved in the organicsolvent, a mass ratio between the pre-polymer and the pre-polymersolution can be greater than a mass ratio between the polymerpolymerized by the pre-polymer and a polymer solution. If the carbonnanotube structure is soaked by the pre-polymer solution and the polymersolution, more pre-polymer can be infiltrated into the intertube spacesthan the polymer infiltrated into the intertube spaces. When thepre-polymer infiltrated into the intertube spaces is polymerized intothe polymer, the composite carbon nanotube structure would be obtained.A mass ratio between the polymer and the composite carbon nanotubestructure of the second embodiment can be greater than a mass ratiobetween the polymer and the composite carbon nanotube structure of thefirst embodiment.

To study and compare properties of the composite carbon nanotubestructure and the carbon nanotube structure, a twisted carbon nanotubewire as shown in FIG. 6 and FIG. 7, can be provided and defined as a CNTwire. The CNT wire can be treated with a volatile solvent to obtain ashrinking CNT wire as shown in FIG. 8 and FIG. 9. The volatile solventcan be applied to soak the entire surface of CNT wire. During thesoaking, adjacent carbon nanotubes in the CNT wire will bundle together,due to the surface tension of the volatile solvent as it volatilizes.

Referring to FIG. 10 and FIG. 11, a composite carbon nanotube wire canbe made by soaking the CNT wire into a polymer solution. The compositecarbon nanotube wire can be defined as a composite CNT wire. The polymersolution can include PVA and DSMO. The PVA dissolving in the DMSO canhave a polymerization degree of about 1750 to about 3300. The contactangle between the DMSO and the carbon nanotubes is about 70 degrees. Thesurface tension of the DMSO is about 43.54 millimeters per newton. Amass ratio between the PVA and the polymer solution is from about 1percent to about 9 percent. In one embodiment, the mass ratio is about 5percent. If the mass ratio is about 5 percent, the composite CNT wirecan be filled with more PVA, and be shrunk by the polymer solution moreevidently.

Referring to FIG. 12, diameters, tensile strengths, and tensile loads ofthe CNT wire, the shrinking CNT wire, and the composite CNT wire arerecorded. The tensile strengths and tensile loads are measured alongaxis directions of the three wires. A shrinking effect of the polymersolution can decrease the diameter of the composite CNT wire, thus thediameter of the composite CNT wire can be less than the diameter of theCNT wire. The shrinking effect of the polymer solution is stronger thana shrinking effect of the volatile solvent, thus the diameter of thecomposite CNT wire can be less than the diameter of the shrinking CNTwire. The PVA loaded by the DMSO can infiltrate into intertube spacesdefined among carbon nanotubes of the CNT wire and firmly integrate withthe carbon nanotubes. The carbon nanotubes of the composite CNT wire canbe joined by the polymer and van der Waals attractive force therebetweenat the same time. The tensile strength of the composite CNT wire can begreater than the tensile strengths of the shrinking CNT wire and the CNTwire. The tensile load of the composite CNT wire can be greater than thetensile loads of the shrinking CNT wire and the CNT wire. Referring toFIG. 13, tensile strengths of the three wires can be recorded when thethree wires have a determined strain quotiety. The tensile strength ofthe composite CNT wire can be greater than the tensile strengths of theshrinking CNT wire and the CNT wire.

Referring to FIG. 14, the tensile strengths of the composite CNT wiressoaked with different polymer solutions can be recorded. Mass ratiosbetween the PVA and polymer solutions can be in a range from about 1percent to about 9 percent. All the tensile strengths of the compositeCNT wires can be greater than about 1.2 GPa. If the mass ratio betweenthe PVA and the polymer solution is about 5 percent, the composite CNTwire can obtain the greatest tensile strength of about 2.0 GPa.

Referring to FIG. 15, the tensile loads and the diameters of thecomposite CNT wires soaked with different polymer solutions can berecorded. The mass ratios between the PVA and polymer solutions can bein a range from about 1 percent to about 9 percent. All the diameters ofthe composite CNT wires can be less than 14.5 micrometers. If the massratio between the PVA and the polymer solution is about 5 percent, thecomposite CNT wire can obtain a diameter of about 12.2 micrometers. Allthe tensile loads of the composite CNT wires can be greater than 200millinewtons. When the mass ratio between the PVA and polymer solutionis about 5 percent, the composite CNT wire can obtain the greatesttensile load of about 233 millinewtons.

Referring to FIG. 16, the tensile strengths and the diameters of thecomposite CNT wires soaked with different polymer solutions can berecorded. Temperatures of the polymer solutions can be in a range fromabout 20 degrees to about 120 degrees. If the temperature of the polymersolution is greater than 50 degrees, the greater the temperature, thegreater the diameter, and the less the tensile strength. If thetemperature of the polymer solution is less than 50 degrees, thediameter and the tensile strength can remain changeless, and thus, themethod for making the composite CNT wire can be taken in a moderatecondition.

Referring to FIG. 17, the tensile strengths of the composite CNT wireshaving different carbon nanotubes can be recorded. The average lengthsof the carbon nanotubes can be about 425 millimeters or about 250millimeters. All the tensile strengths of the composite CNT wires can begreater than 1.5 GPa, even if the lengths of carbon nanotubes of thecomposite CNT wire and the diameters of the composite CNT wires aredifferent from each other.

Depending on the embodiment, certain of the steps of methods describedmay be removed, others may be added, and the sequence of steps may bealtered. It is also to be understood that the description and the claimsdrawn to a method may include some indication in reference to certainsteps. However, the indication used is only to be viewed foridentification purposes and not as a suggestion as to an order for thesteps.

It is to be understood that the above-described embodiments are intendedto illustrate rather than limit the disclosure. Any elements describedin accordance with any embodiments is understood that they can be usedin addition or substituted in other embodiments. Embodiments can also beused together. Variations may be made to the embodiments withoutdeparting from the spirit of the disclosure. The above-describedembodiments illustrate the scope of the disclosure but do not restrictthe scope of the disclosure.

What is claimed is:
 1. A method for making a composite carbon nanotubestructure, comprising: providing an organic solvent and a polymer;dissolving the polymer in the organic solvent to obtain a polymersolution; and applying a carbon nanotube structure in the polymersolution to composite the polymer and the carbon nanotube structure, thecarbon nanotube structure being a free-standing structure and comprisinga plurality of carbon nanotubes, a contact angle between the organicsolvent and the carbon nanotubes being less than 90 degrees.
 2. Themethod of claim 1, wherein the contact angle between the solvent and thecarbon nanotubes is less than or equal to 70 degrees.
 3. The method ofclaim 1, wherein the organic solvent has a surface tension greater thanor equal to about 20 millimeters per newton.
 4. The method of claim 3,wherein the surface tension of the organic solvent is greater than orequal to about 40 millimeters per newton.
 5. The method of claim 1,wherein the organic solvent is selected from the group consisting ofdimethyl sulphoxide, dimethyl formamide, 2,5-dimethyl furan, andcombinations thereof.
 6. The method of claim 1, wherein the polymer isselected from the group consisting of polyacrylonitrile, polyvinylalcohol, polypropylene, polystyrene, polyvinylchloride, polyethyleneterephthalate, and combinations thereof.
 7. The method of claim 1,wherein the polymer is polyacrylonitrile, the organic solvent isdimethyl sulphoxide, and a mass ratio between the polyacrylonitrile andthe dimethyl sulphoxide is from about 1 percent to about 9 percent. 8.The method of claim 7, wherein a polymerization degree of thepolyacrylonitrile is in a range from about 1750 to about
 3300. 9. Themethod of claim 1, wherein the carbon nanotube structure comprises acarbon nanotube wire, the carbon nanotubes of the carbon nanotube wirebeing joined end to end by van der Waals attractive force therebetween.10. The method of claim 9, wherein the carbon nanotube structurecomprises a plurality of carbon nanotube wires substantially parallel toeach other, crossed with each other, or woven together.
 11. The methodof claim 9, wherein the carbon nanotube structure comprises a pluralityof carbon nanotube wires substantially parallel to each other, orcrossed with each other, adjacent carbon nanotube wires are combined andattracted to each other by van der Waals attractive force therebetween.12. The method of claim 9, wherein the carbon nanotubes of the carbonnanotube wire are substantially oriented along an axis of the carbonnanotube wire.
 13. The method of claim 9, wherein the carbon nanotubesof the carbon nanotube wire are helically oriented around an axis of thecarbon nanotube wire.
 14. The method of claim 1, further comprisingvaporizing the organic solvent from the composite carbon nanotubestructure composited by the polymer and the carbon nanotube structure.15. The method of claim 14, wherein a mass ratio between the polymer andthe composite carbon nanotube structure containing the polymer is in arange from about 2.5 percent to about 21.5 percent.
 16. The method ofclaim 1, wherein the polymer is infiltrated into intertube spacesdefined in the carbon nanotube structure.
 17. The method of claim 1,wherein the intertube spaces comprise spaces defined among the carbonnanotubes and spaces defined by inner surfaces of the carbon nanotubes.18. A method for making a composite carbon nanotube structure,comprising: providing an organic solvent, a pre-polymer, and a carbonnanotube structure, the carbon nanotube being a free-standing structureand comprising a plurality of carbon nanotubes, a contact angle betweenthe organic solvent and the carbon nanotubes being less than 90 degrees;dissolving the pre-polymer in the organic solvent to obtain a polymersolution; soaking the carbon nanotube structure with the pre-polymersolution; and polymerizing the pre-polymer infiltrated into the carbonnanotube structure to obtain a polymer.